This invention is in the field of printing equipment and is concerned with a method and apparatus for controlling the operation of such printing equipment wherein the said equipment includes a plurality of printing elements all operating on a moving web to apply respective images to the web in different colors, for example. Each printing element has a set of operating parameters each of which must be adjusted and controlled, and the sets of parameters have some relationship with one another to the end that the final result upon the web will represent a properly registered pattern.
The method and apparatus of the invention are directed to a concept in which the parameters are recorded on an information carrier and identified with a particular project or pattern so that when it is desired to repeat that project or pattern the carrier is used to achieve the desired setting up of the printing equipment. Thus time and materials are saved. Furthermore, the information on the carrier is not static but can be varied by the measurement and comparison of the same with parameter readings taken as the apparatus is being used continuously to maintain the best information.
Although the measures according to the invention may be used in any known printing equipment or apparatus, particular advantages are obtained when using the measures provided by the invention in a rotary screen printing machine having a system wherein a plurality of cylindrical screens is supported and means are provided for setting the position of the screens: in the direction of travel of the material (longitudinal relationship); in transverse direction (transverse relationship), and in diagonal direction (inclined adjustment), as well as for effecting the angular adjustment of the squeegee for each screen, adjustment of the pressure applied by the squeegee and of the location of the squeegee in the direction of travel of the print-receiving material, means for setting the paint level in the respective screens, and means for adjusting the glue and water film thickness on the printing blanket.
This type of printing apparatus with adjusting mechanisms, belonging to the state of the art, is described in Dutch patent application No. 7,511,692. Adjusting means for the individual screens and the associated squeegee are described in Dutch patent application No. 6,910,511 and are not further explained herein. These mechanisms and means afford the accurate adjustment of the position of the respective screen in the longitudinal and transverse directions as well as in a direction diagonal with respect to the moving band and the web material supported thereon.
Each screen is furthermore provided with means, likewise belonging to the state of the art, for axially tensioning the screen, there being disposed in each screen a squeegee with a mechanism for adjusting the position of the squeegee, likewise belonging to the state of the art and described in Dutch patent application No. 7,103,481.
Such a printing apparatus will obviously be used in conjunction with auxiliary equipment for the feeding of the web material to be printed, an arrangement for carrying out the steam treatment of the printed web material for the purpose of fixing the colorants, and control and regulating equipment.
As said, a printing apparatus such as described hereinbefore is provided with many adjusting mechanisms for effecting the following adjustments:
position of the screens in: PA0 (a) the direction of travel of the material (longitudinal relationship) PA0 (b) the transverse direction (transverse relationship), and PA0 (c) the diagonal direction (inclined position), and for each screen: the angular setting of the squeegee, the pressure at which the squeegee rests upon the inner surface of the screen and the paint level in the respective screens. Such adjusting mechanisms are, as said, part of the state of the art. PA0 (1) Position of the screens with respect to one another as measured in the direction of travel of the print-receiving material (i.e. longitudinal relationship). PA0 (2) Adjustment of the screens in a direction parallel to their axis of rotation (i.e. transverse adjustment). PA0 (3) Adjustment of the tangent between the screen and the print-receiving material in order to obtain a proportioning in the event of inaccuracies if any in the patterning (i.e. inclined adjustment). PA0 (4) Adjustment of the angle of the squeegee blade, which affects the quantity of printing ink (paint) applied during the printing process. PA0 (5) The pressure of the squeegee. In textile printing, the mechanical force of pressure applied determines to a large extent the penetration of the printing paint into the material. PA0 (6) The location of the squeegee as measured in the direction of travel of the print-receiving material. In addition to influencing the quantity of printing paint applied, this setting is also a determining factor for the mechanical pressure of the screen. PA0 (7) The level of the printing paint in the screen. At a constant viscosity, the paint level has some influence on the paint yield as a result of the hydrostatic pressure. PA0 (8) Thickness of the glue layer on the printing band. PA0 (9) Thickness of the water film after the band-washing device.
In the case of the known printing apparatuses, these adjusting mechanisms consist of manually operated means, for example handwheels which are coupled to the various adjusting devices by way of knurled wheels, transmission belts or flexible shafts. The form of embodiment to be described according to the subject application utilizes, for the adjusting mechanisms, servomotors which are known per se and not further explained herein, and which may be controlled either by manually operated switching devices, such as push buttons, or by suitable electric circuits, and whose shaft extending therefrom can be driven rotatably, clockwise or counterclockwise, under the influence of an appropriate control command; each servomotor is coupled to a sensor which indicates the instantaneous position of the shaft and thus the parameter value. Such apparatuses are known as such in many different forms (optical, mechanical, inductive) and so will be described hereinafter in a general manner only.
The parameters which are adjusted by means of the apparatus described hereinbefore are as follows:
In general, there is provided in a rotary screen printing machine for the printing of fabric-like materials whose dimensions are not very stable, a conveyor band supporting and moving the material to be printed. To ensure tight positioning and prevent displacement, a temporary glue film is frequently applied to said band by means of a glue applicator, a washing device removing, at each revolution of the band, the glue film to the extent this may still be present, the glue film to be subsequently applied again. The thickness of the glue film is of importance to the quality of the material printed. Displacement may occur if the film of glue is too thin, whereas, if the glue film is too thick, there will not only occur an unnecessary waste of glue but it may adversely affect the penetration of the printing paint brought upon the material to be printed.
Even if there should be no temporary glue layer to be washed off, it may still be necessary to remove, with each revolution of the band, the printing paint which during the printing of the fabric penetrates down to reach the conveyor band. It is important to control the water film originating from the washing device and left on the band. This water film may affect the glue layer to be applied as well as the penetration of the printing paint to be applied during the printing process.
It is known to control a printing apparatus having a series of print elements, such as screens, which as to the operating parameters are individually adjustable, the parameter values as determined for the first print job format being recorded on an information carrier, and said information being read out for a repeated print run of the same pattern to be carried out and being used to adjust the various parameters. The method is disclosed in Dutch patent application No. 7,511,692. The object of this known method is to speed up and simplify the manual operations needed for the initial setup of a printing apparatus prior to performing a printing job wherein a certain pattern is printed on a web of moving material by means of a number of print elements. To this end, particulars pertinent to the respective operating parameters to be set are recorded on a record card pertaining to the particular pattern, said particulars being used to set the operating parameters of the various print elements prior to performing a repeated print job.
The first printing of a new pattern requires that all the various parameters of the successive screens be set in a manner so that the end product is of optimum quality. It has been known that in most cases such adjustments will differ from the respective initial reference adjustments. In the case of the known printing apparatuses the procedure is such that, when optimum results have been attained with the first print job, the adjustments of the various parameters are noted and recorded on the information card; when after a certain time the same pattern is to be printed again on a certain amount of material, this card, which has been preserved and which bears also the pattern designation, is used to adjust, before actually starting the running of the printing apparatus, the parameters in accordance with the values recorded on the card.
Although this method provides an improvement on traditional methods, it is by far not the best method, and maximum accuracy and speed of adjustment are certainly not attained. In order to obtain the best possible settings it is necessary to effect a number of operations manually while visually observing the printing results obtained and having already started the printing process. In addition, it is necessary to preserve the record card for each composition of colors used for each particular pattern and, when repeating the pattern, to place it in the proper position and view it, while it is necessary to use mechanical adjusting means so as to approximate the optimum settings desired.
The invention not only further simplifies the procedure of adjustment by using a special method for recording the various parameter values which at any moment desired can be read out again and be used to control the various settings but also by effectively taking advantage of the possibilities offered by modern digital techniques for controlling the printing apparatus. According to the invention, the process takes place in a manner so that the various parameter values are converted into a digital form and this information together with information characterizing the respective pattern is recorded on a suitable carrier, these data being read out at the beginning of a print run to be repeated of said pattern and used to carry out the various parameter adjustments.
It is evident that in this manner quite substantial savings both in time and in material are obtained, since all information relative to a certain pattern and the corresponding adjustments of the print elements can be recalled in a very short time and the adjustment of the various parameters can be effected at practically the same moment.
Due to some slight play in mechanical transmissions, dimensional differences caused by tolerances, elongation and other mechanical changes, it may happen in practice that after a number of print runs the optimum settings then valid differ from the optimum settings originally found. According to the invention, this is taken into account in that, during a repeated print run, new parameter values being used and deviating from the original parameter values are brought onto the information carrier to replace the original values.
The known method proceeds in a manner so that, when for the first time determining the parameter settings for a new pattern based on the reference positions of the print elements while simultaneously evaluating the printing results obtained, the optimum settings are approximated. Obviously, such procedure leads to a large waste of material in that, also because of the large number of adjustments to be effected, the ultimate optimum adjustment is only slowly approached. According to the invention, this optimum adjustment can be found much faster in that, during the operation of the printing apparatus, for each print element the individual differences of the printing parameters with respect to the reference parameter values as determined by the construction of the apparatus are observed and the average of these differences is determined and recorded, and, when carrying out for the first time a print job with a series of print elements for another pattern, the initial parameter adjustments of each one thereof are chosen in conformity with said average differences.
Consequently, the differences arising during the operation of the printing apparatus relative to the reference values are taken into account immediately upon starting the print run of a new pattern, as a result of which the ultimate optimum adjustment is attained considerably faster.
Since, when properly positioning an adjustment possibility controlling the printing process, it is customary to follow a predetermined sequence, i.e. the same sequence as followed for placing the screens into the rotary screen printing machine as viewed from the direction of printing, there is a possibility that, already before all adjustments controlling the same parameters for the various screen positions have been effected in a certain position, the end of the range of adjustment possibilities available in one direction will be reached.
The invention solves this problem by proceeding in a manner so that, when adjusting for the first time the registration relationship parameters of the print elements beginning with the first of each print element, the dimensional and directional difference, needed for optimum results, with respect to the reference value is observed, comparison is made with that for the next print element and the remaining adjustment margin thereof is ascertained, and, when for a parameter of a print element the limit of the adjustment margin in a particular direction is reached, the parameter adjustments of the preceding print elements are changed in opposite direction so as to increase the range of adjustment still remaining for the following print elements.
A problem frequently occurring in practice is that it may happen that adjustments have been going on on a machine in operation for some time already before it is noticed that it is impossible to set certain parameters at the proper value due to an error in, for instance, the placing of the screens or the fastening of the end rings or due to the wrong placing of the squeegee blade. This may result in a great loss in the printed product.
This drawback is eliminated according to the invention in that prior to starting a print run it is checked for each parameter recorded whether the latter can be set at the proper value and, failing this possibility, the starting of the printing process is blocked.
Preferably, each adjusting and control member is regularly checked as to its proper functioning.
When feeding parameter value data, a key board is preferably used having keys representing certain functions so as to prevent errors and illogical manipulations from occurring.
Furthermore, when setting a parameter value for various print elements, the value desired is always passed in the same direction and is subsequently returned to the final value desired, thus providing the advantage of eliminating play, if any, always in the same direction.